It always did sound a little too good to be true.
Now claims that following a 'grapefruit diet' helps you lose weight without exercising have been well and truly squashed.
The news may leave a sour taste in the mouths of celebrities such as Brooke Shields and Kylie Minogue, who have championed the fad diet.
Invented in the 1930s, it is based on the idea that grapefruit contains a fat-burning chemical. This apparently meant that dieters who ate plenty of it would be spared having to go to the gym.
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But scientists have now found that while the chemical naringenin does exist, you would need to scoff at least 40 grapefruits in one sitting for it to have any impact. And even if someone managed this feat, it would mean they had consumed 5,000 calories or a kilogram of sugar - outweighing any health benefits. The diet comes in various forms. Some eat a portion of grapefruit before each meal without changing any other part of their routine, while others combine it with cutting down on starchy foods and carbohydrates.
But professor Yaakov Nahmias, who carried out the latest research at the Hebrew University in Jerusalem, said those who lose weight on the diet are more likely to achieve this by reducing their overall number of calories while following it, rather than from any special property of the fruit.
He added that when the body ingests naringenin, it believes it is fasting and starts breaking down fat. But as the chemical is not easily absorbed, a person would need to eat "something in the order of 40 grapefruit" to benefit.
"It's going to be a bad, bad idea," Professor Nahmias says in Channel 4 documentary Superfoods: The Real Story.
Dr Duane Mellor, of the British Dietetics Association, said last night: "Nutritional science is complicated - we shouldn't be looking to celebrities for fixes.
"If you are eating well and exercising, then that is healthier than trying to achieve some sort of celebrity ideal that is, for most people, unattainable and probably unhealthy."
- Daily Mail